corundum, treatments.6, gems

Gunawardene reports observations on yellow sapphires produced by heat treatment, particularly material from Sri Lanka. The paper examines changes in colour resulting from heating and the gemmological features that may assist in recognizing treated stones. Of particular interest is the behaviour of the induced yellow to orange-yellow colour under subsequent heating and illumination, together with microscopic evidence of thermal alteration. The study contributes to the developing understanding during the 1980s of how heating could produce or modify yellow coloration in corundum and of the practical difficulties involved in distinguishing such stones from naturally coloured yellow sapphire.